We evaluated the efficacy of clonidine given orally preoperatively for preventing postoperative vomiting (POV) in children undergoing propofol-nitrous oxide anaesthesia for strabismus surgery. Sixty children, ASA physical status I, aged 2–12 years, received diazepam, 0.4 mg·kg–1 or clonidine 4 μg·kg–1 (n=30 each) orally, in a randomized double-blind manner. These drugs were given 105 min before an inhalational induction of anaesthesia. A complete response, defined as no POV and no need for rescue antiemetic medication, during 0–24 h after anaesthesia was 67% with diazepam and 93% with clonidine, respectively (P=0.024). No clinically adverse event was observed in any of the groups. In summary, pretreatment with oral clonidine enhances the antiemetic efficacy of propofol for the prevention of POV after paediatric strabismus surgery.